Automatic dimpler



March 30, 1948. E, v CHRISTENSEN 2,438,842

AUTOMATIC DIMPLER Filed March 7, 1944 3 Sheets-Sheet 1' INVENTOR. FEW/WV TZ'CHHETENSEN BY Z AGENT March 1948' E. V. CHRISTENSEN 3 ,842

AUTOMATIC DIMPLER Filed March 7, 1944 3 Sheets-Sheet 3 I N V EN TOR. Ezwm/ Vimzsrmwzzv Patented Mar. 30, 1948 AUTOMATIC DIMPLER Edwin Christensen,

to Lockheed Aircra Calif.

Hollywood, Calif., assignor ft Corporation, Burbank,

Application March 7, 1944, Serial No. 525,412

9 Claims.

This invention relates to automatic dimpling and riveting machines in general and more particularly to the automatic control of machines for countersinking rivet holes or bolt holes in pie-punched or drilled sheet metal in the manner commonly employed for flush riveting airplane skin panels.

This invention may be adapted to numerous uses but finds its principal application in automatic dimpling or countersinking tools wherein the weight of a properly positioned sheet metal skin panel initiates the dimpling action. The present invention is primarily directed to the form of dimpling tool embodying automatic actuation and control and suitable safety mechanism which allows actuation of the machine only when the pro-punched or drilled sheets have been located in precisely the correct position Within the machine for the forming operation, preventing thereby inadvertent operation of the dimpler prior to proper location of the sheet, and also to prevent repetition of the dimpling operation at a single dimpling location.

Various forms of dimpling tools have been heretofore employed for use with either one shot or diaphragm types of rivet squeezers. As customarily operated, these dimplers have a footswitch or an air valve to be manually actuated by the operator after he has located the hole in the sheet over a pilot pin in the dimpling die.

With such manual operation of the squeezer mechanism it is possible for the machine to be actuated prior to proper location of the work sheet in the machine or during the step of shifting the Work sheet from one work position to another, and thus inadvertent operation of the machine often occurs accidentally, apparently due to momentary lapses of proper coordination of the operator, probably brought about by the fatigue associated with rapid operation. Such inadvertent operation of the machine usually results in serious damage to the work piece and at times injury to the operator.

It is accordingly an object of this invention to eliminate the usual manual controls employed for operation of the squeezer thereby reducing fatigue and giving the operator greater freedom of movement and facility of handling the work sheet applied to the dimpling machine. It is another object of this invention to furnish an automatic means to actuate the dimpling or squeezing tool when the Work sheet is in the proper location. It is a. further object to furnish a practical safety means to prevent inadvertent actuation of the machine while the work sheet is improperly located. It is a still further object of the present invention to provide automatic actuation oi. the machine of such character as will produce uniform work independent of the skill of the operator.

The objects are attained in general by an embodiment of the invention which includes an automatic, fool-proof, mechanism associated with the die and punch mechanism which renders the squeezer machine inoperative unless the work sheet is in its precisely correct position between the die and punch and which will then substantially automatically initiate the actuation of the punch largely by the weight of the work alone when the work sheet is so located,

The objects of this invention are also attained by novel electrical timing and control means associated with the before mentioned automatic die and punch mechanism.

These and other objects and features of novelty will become evident hereinafter in the description which, together with the following drawings, illustrate preferred embodiments of the invention.

Figure 1 is an elevation of a typical squeeze dimpler showing the general arrangement of the apparatus of this invention therein.

Figure 2 is an elevation of the dimpling head assembly as viewed on line 2-2 of Figure 1.

Figure 3 is a plan view of the dimpling head assembly as taken on line 33 of Figure 1 and Figure 2.

Figure 4 is a sectional elevation of the dimpling head taken on line 44 of Figure 2 and including a schematic representation of the associated electric control circuit.

Figures 5, 6 and 7 are fragmentary sectional elevations of the punch and the dimpling die head of Figure 4 at several stages of its operation.

Figure 8 is a fragmentary sectional elevation of an optional form of dimpling heads.

Figure 9 is a schematic wiring diagram of an alternative control and timing circuit.

Referring now to the drawings in which like reference numerals refer to corresponding parts throughout the several figures, the apparatus of the invention is as follows:

The apparatus of this invention as employed in connection with a conventional squeezer machine-is shown in Figure 1, said machine comprising a yoke Iii having upper and lower jaws H and I2, and supported on a pedestal l3. On the upper jaw H is a diaphragm cylinder M, the diaphragm piston of which is operatively connected through suitable linkages to the reciprocable punch holder IS. The automatic die holder head which comprises a principal part of the invention is supported in the lower jaw l2 of the squeezer yoke in operating position as shown at I6 directly beneath the said punch holder 15. In operation the pre punched or drilled sheet is introduced into the machinepbee tween thepunch anddie set as-shown-at I! in- Figure 1.

Air under pressure from a suitable source issupplied to the diaphragm cylinder [4, by pipes: 18 and [9, through a pilot operated control valve 20. The pilot valve 20 is adaptedito'becontrolled by the variation of the pressure of air in pipe,- 2| by a solenoid operated air valve V as hereinafter more fully described.

The electric timing circuit is contained within a box 25 mounted on the squeezer pedestal l3; and the before mentioned solenoid controlled valvecis housed: in :a;box=.26 which may be. placed? ineanyrconvenient;location; Airl under: suitable:

pressure is: supplied; to: the: solenoid valvea-v: in;

b03126; from a suitable-source through-pipe 237 The electric lea-d wires interconnecting :the electrlc control circuit and the solenoid" operated Valve; pass: through asuitable shielded :conduit as sh'own at 28; The-electricaltconductors from the-electriccontrolcircuit in box 25 pass through: a suitable shielded :conduit 29 to a terminal box: 30 intowhiclr the lead--31 containing conductors- H? 11 and la fromthe automatic head l6,makes-' a--plug-connection-as shown zit-32:

Referring now-primarily; to Fi"gure 4;- the bodyo f the automatic dimpling-hea'd' lt 'comprises an uppercylindrical di'eholder-portiomfl a lower cylindrical shank 42: joined by an intermediate 7 The shank 42 is; adapted to fit into the die-holding recess in'the' circular supporting collar- 43-.-

low f l' aw l 2-, of-the squeeze dimpler; and Ice-supported "by collar 43; as;b est shown in Figures-- 1" and25i, The upper cylindrical ;surface:of-=the die:

holder portion serves as a guide for reciprocably supporting a semigcylindrical sleeve dd-whioh carries at-the upper end a semi-circularchamfered'cuff'or ring member 45; WhlChjCOflStl'tlltES" one of the trigger members for;automatic-actuation Off HGIGGViCB'a-S hereinafter-more fully described; A The. cuff. or ring member AEJhas-amutaway opening as best shown at-46 in Figure 2, which forms thereby at its lower edge, a bridging ciECular; segmental element 33, through ewhich isthreaded an adjustable switch actuating screw-41.

Theesemi-cylindricali sleeve 44 is normally; urged'upward to the extendedjposition shown inlligures 2, and 4, by springs, I 03 ,acting under compression between win s I llfl'exten-ding later: ally ,from the, lower edgeofg the sleeve. 44; and; the bottom of the cylindrical recesses lill in the supportingcollar 43. 7

Stop screws 1 fla threadedjini oothe body, 4'! and actin inilonsitudinalslots!051m,tne sleev -4; serve to limit thalon itudinallmovementoifvhei sleeves-5. V

A dimpling diecswhich-hastaflsmalliaxiakborc- 4 9 is supported at theuppernendfioi the die hold er 4| in a cylindrical recess-B1. lnwardlmo eg. mentmf-the dimplingdieB into ,th,e upper end of ;ther holder, A ,islimited by w the, annular shoul: V deriiil Within the coaxial" bore 531 of the body iith i dieiholcle l 4 1-4215 ;a re ipr ca e lin: i it l pl nscrfii he pe n of fi h'ep uneerz 4..,n .rries-.- n integrallulormed pilot i Wh q ism sufficient l n thi r extend .throu hithe. 11:"-

tral bore 49 of the before mentioned dimple die to a point above the upper surface of the ring 25 when the plunger and the said ring are in their uppermost positions as shown in Figure 4. A coil spring 56 acting under compression between 5 the lower end 58 of the plunger 54 and the upper shoulder 59 of a threaded adjusting screw 60, serves normally to maintain the plunger 54 in its extreme; upper position, with the-upper end 6! of -the pilotpin 55 extending out through the dimple die as shown in Figure 4 as just mentioned. An upper cylindrical extension 62 of the adjusting" screw 60 serves as a guiding support for the coil spring 56 and also as a stop to limit thexiownwardmovement of the plunger 54.

A switchactuating pin 63 extends laterally from the intermediate portion of the plunger 54 through an axialslot 6% formed through the die holder body in which the pin 63 has freedom for limited longitudinal motion upon reciprocation of the plunger 54. Two micro-switches $5 and 6t; separatedia suitable distance apart, are :fixed to thezdie holderobody: ll on'flatiseats Stand 58 thereon; by means of screws 69. and ill. These micro-switches mayibe'of'any one of several well known types aandrmanufacture; such as, for example; the- General Electric; CR1070-C103E3. The actuating plungers fOIrtl'lt-l micro-switches: are shown at?! and 13 with which the adjustable actuating screw M and the are respectively adapted to: contact aspin 63 hereinafter more fully described'in connection with the operation of: the apparatus; Inward and outward motion of the micro-switch plung ers serveto close and open the contact points 5- therein to respectively complete and break the circuits therethrough.

The micro-switches 65 and 66" when employed as-shown in Figure 4; are connected in series by means of "a common interconnecting conductor 15: Three lead conductors 16, El and 13 are brought out from the micro-switchestti and 6t, and from the said common-interconnecting conductor 75 respectively, which leads make connection withtheactuator and the control circuit diagrammatically illustrated in connection withFigure 4.

In the schematic wiring diagram shown in Figure-4; Xi is a double pole single throw magneticrelay-which is-normally maintained open by spring'fifl; X2 is a single pole doublethrow magnetic time delay relay switch normally held inthe position shown; by the spring 81; and

X; is: a; single pole single throw magnetic relay normally held open by the spring 32. S is a solenoid adapted to actuate the air" valve V through the interconnecting link 83. Terminals 8 and 85 lead-ingto the circuit are provided for connection to a suitable current supply, preferably direct current'such as a battery or a direct currentgenerator.

The action of the electrical control circuits diagrammatically'shown in connection with Figure-A ilIbcmQre fully described herein in connection With the operation of the invention which is 'asiollows:

Uponfirst locatingthe pre-drilled sheet ll to be dimplediin place between the dimpling punch 9| and the dimple die-48 of the tool, and allowing its weight first to rest upon both the end 6i of the pilot pin 55vandthe upper surface ofthe ring member 45, the average sized sheet will ordinarily be, sup ported by the pilot pin without deflection of the ring memberfi5, but both the said pilot pin 5 5jandj thje ring i5jmay, with slight downward assisting pressure-upon Switchette, No.-

the sheet "by the operator;

be retracted to the positions shown in Figure and the sleeve 44 carrying the ring 45 will then be depressed against the action of springs I03 bringing the end of adjusting screw 41 in contact with the actuating plunger I2 of the micro-switch 65. The plunger 55 will also be depressed against the action of spring 56 to the position shown in Figure 5, resulting in movement of the lateral pin 63 away from contact with the actuating plunger I3 of the micro-switch 66. Micro-switch 65 will thus be closed while at the same time microswitch 66 will be opened. The circuit through the micro-switches which are connected in series with the conductors I6 and I! will thus remain open, and since the middle conductor I8 leading from the common connection between the microswitches leads to an open contact point 86, no actuation of the circuit then takes place under these conditions. With the sheet I! positioned in the tool and resting on the pilot pin end BI and upon the ring trigger member 45 as before mentioned, the sheet may be supported there without actuation of the switches 65 and 66, but as soon as a pre-drilled hole 92 in the sheet 90 is adjusted into registration with the pilot pin 55, thesaid pilot pin immediately snaps up through the hole to the position shown in Figure 6 allowing the plunger 54 to rise, carrying the pin 63 up into contact with the micro-switch plunger 13 to close the contact of micro-switch 66, and allowing the sheet II to lower against the forming surface of the die 48 against the resistance 01' the ring trigger member 45, The screw 41 is thus brought into contact with the plunger 12 of the micro-switch 65. The sheet I! is then in its precisely correct location for dimpling, as shown in Figure 6 and the series circuit through both the micro-switches 65 and 66 is then complete. The current can then flow from the current supply connected to terminal 85 through bus I05, lead-wire I6, micro-switch 65, interconnecting wire I5, micro-switch 66, lead-wire I1 and thence throughconductor I06 through the electro-magnet I01 of the relay X2 and from'there through conductor I08 and return to terminal 84 through bus I09.

If desired, the spring 56 opposing the retraction of the pilot pin 55 may be adjusted for sufiicient opposing force to support the weight of the work sheet I I on its end 6I without retraction. Under this condition in operation, the work sheet is adjusted until a perforation registers with the pilot pin, at which time the sheet drops onto the ring 45 depressing it and actuating the switch 65.

Current also simultaneously flows from conductor I06 through the armature IIO of relay X2 to contact III and thence through conductor II2, electro-magnet II3 of relay X1 and through conductor II4 to bus I09. The electro-ma-gnets of relays X1 and X2 are thus simultaneously energized and the interlinked armatures H5 and H6 of relay X1 are immediately closed to contacts II! and H8. The circuit from the power supply is thus initially completed between the busses I05 and I09 through the solenoid S by Way of conductor I20, relay armature I I6, contact I I8 and connections I2I and I22.

Simultaneously upon energizing the solenoid S as just described, the electro-magnet I23 of relay X3 is also energized from the power supply by way of bus I05, lead conductor 16, micro-switch 65, connection I5, micro-switch 66, lead connection I7, conductor I25, relay armature I I5, contact point Ill, and conductors I26 and I21 and return to bus I09. The armature I28 of relay X3 is thus next closed to make contact at I29 return to contact I29.

Upon closing the circuit through the solenoid S as hereinbefore described, the valve V is actuated to admit low pressure air through pipe 2I to the pilot control valve 20 which in turn serves to admit high pressure air from pipe I8 through pipe I9 into the top end of the diaphragm of the diaphragm cylinder I4 which in turn, by means of suitable mechanism in the upper jaw of the squeezer yoke causes the dimple punch holder I5 carrying the punch 9i, to be lowered into contact with the sheet II on the dimple die head to form a dimple.

Upon thus lowering the punch GI upon the sheet in the dimple die to form the dimple in the sheet, the punch' pilot pin I 35 is brought into contact with the top end 6! of the pilot pin 55, forcing it together with the plunger 54 downward within the die holder 4! against the action ofthe coil spring 56 to the position shown in Figure 7. The lateral pin 63 is thus moved away from contact with the micro-switch plunger I3 and upon completion of that dimple the micro-switch 66 is then opened. However, since the micro-switches I55 and 66 are now bridged by means of the relay X3, as before mentioned in connection with the operation of relay X3, this opening of the micro switch 66 will have no effect upon the circuit at this time.

Meanwhile, the armature I I0 of the relay X2 has been moving toward the contact 65 under the force of the energized electro-magnet I43! at a retarded speed as determined by the bellows I36. The contact point III, being on a spring support, follows in contact with the armature IIO until contact is made with 86. This contact between armature lit and contact 86, then bridges the micro-switch 66 by way of conductors I8 and 'IS, micro-switch 66, conductors TI and IE6, armature III? and return to contact 86. The circuit through the electromagnet I07 of the relay X2 is thus perpetuated from bus I05 through line I6, micro-switch 65, connections I5 and I8, contact 66, armature I10, coil I6! and through connection I63 and return to bus I09.

Soon thereafter, by reason of the continued movement of the armature I50 against the retarding force of bellows I36, the contact between point III and the armature iIll opens, and the electro-rnagnet H3 of relay X1 is then de-energized, in turn opening the contacts III and I53. The solenoid S is thus neXt tie-energized, allowing the valve V to return to its closed position, moving the pilot valve 26 to exhaust the pressure from the top of the diaphragm and allowing the dimple punch 93 and punch holder I5 to return to their open positions as shown Figure 1. The electro inagnet I26 of relay X3 is also simultaneously die-energized upon the opening of contact ill. in turn resulting in the opening of contact between the armature I28 and contact point I29.

The opening of contact between I23 and IE5 removes the shunt across the micro-switches 55 and but the time has been such that the micro-switch has now been again closed by the upward return movement of pin and plunger 54, and. as long as the mim c -switches 55 remain closed by he weight of the sheet I? supported upon the ring 45, the electro-magnet I 01 'of;the relay X2 will. remain energizedby way of circuits I05; lead 16, micro-switch E5,=- connection it, lead 78, contact 85, armature! lllfiand conductor B08 leading to bus I09;

Now upon opening of the micro-switch tb effected by the removal of the weight ofsheet I? from. bearing upon the ring 45; the circuit tion, the electric control circuit andthe squeezermechanism is then ready for repetition of the operating cycle just described.

It will be obvious that the characteristicsof this electrical control circuit are such that upon.

actuation of the squeezer in the formationof a dimple-as shown at iii! in Figure l, 2, reactuation ofthe dimpler cannot'be immediately effected but instead, there is ashort delay period during-which time movement of thepilotpin 55- and/or the. ring member is willnot ire-energize the circuitto again set the squeezer inmotion; A period of readjustment of the sheet to be dimpledisthus allowed, and after it ismoved.

to a new position the squeezer cannot be again set intomotion-until the ring ie'has-beende pressed and precise registry of the sheetihole to be dimpled is made over. the pilot pin 55 in position between the dimpling punch and die as shown in Figure 6.

Referringnc-w primarily to Figure 9. in which an alternative electronic control circuit is diagrammatically illustrated, the principal componentsthereof are as follows: T1 and T2 are vacuum tubes which may be of substantially any ofthewellknown suitable types. For example, a type 6N7 tube which is a twin triode containing the. elements of the two tubes in one envelope, may be. advantageously employed, although for. convenience two/separate tubes are herein illustrated. double throw and double pole single throw magnetic relays respectively. C1 and C2 are condensers, and resistors of suitable values are shown at R1, R2, R3 and R4. The high voltage supply for the plates or the vacuum tubes is suppliedfrom a. suitable source of approximately 150 volt D. C. such as a battery B and a negative. grid bias of approximately 5 volts isobtained from a suitable battery C. Suitable variation in these voltages may be made as is well known in the art.

In the. electronic circuit the. micro-switches fid-and 56 and the pilot pin 55'and ring- 35 hereinbefore described in connection with Figure 4 are shown diagrammatically at A.

The operation oithe, automatic squeezer shown.

in Figure 4: in combination with the electronic control circuit of Figure 9, is as-follows: When the squeezer is not in operation and the electronic circuit is quiescent, the vacuum tubes T1 and T2 are maintained non-conductive or at a low conductivity by reason of their grids G1 and G2 being biased to out Oh or close to the cut-01f potential by the C battery. Under this initial condition, condenser C1 is charged to avoltage at or approximating the. grid cut-ofi;potential of;tube T1. Upon closing the micro-switch 65 as,;hereinbefore described,,the-charge on; cone S1 and- S2. are single poledenser C1 isdischarged through current-limiting resistance R2 and conductor l6, micro-switch 65,

connection 15, micro-switch t6, and-connection TI to ground. Resistance R1 being high in the neighborhood of 500,000 to-1,000,000 ohms, the

battery C cannot'restore or maintain the charge in condenser C1 so long as this circuit to ground through the micro-switchesis maintained. The

grid G1 is thus lowered to substantially cathodearmature MES-into contact with point 208. Thegrid G2 of vacuum tube T2 is thus next connected through conductors 269 and M0 to the condenser 02 which is initially at ground potential by reason of its having been previously bridged by resistance R3 which is connected to ground at 2| I. The grid. G2 is thus also next momentarily reduced to substantially cathode potential which immediately renders tube T2 sufficiently conductive to operate relay S2. The values of the resistance R4 and the capacity of Czare such-as to prevent return of the g rid'to cut o-ii potential for a suitable period of time. For example, a value of 750,000 ohms for R4 and 0.5 microiarads for C2 willresult in a time constant of approximately 0.1 to 0.5 second for the timing circuit. The

the solenoid S by way ofconductors Zieand 2 ll, 7

whereby a current flows therethrough from a suitable source which may be connected at 218- andv 2i9.- The resultant actuation of the valve V- through linkage fiscauses the dimpler punch 9! to be loweredsinto contact with the sheet to-be dimpled'on thedhnpling die in the manner as:

hereinbefore described. The resultant contact of the punch pilot pin I35 upon the upper end 6! ofthe pilotpin-55 results in the opening-of the micro-switchfifi as hereinbefore described. The opening of the micro-switch E5, however, does not immediately result in any action within the electronic circuit, for the reason that the beforementioned movement of the armatureZlZ.

into contact withthepoint 2M has shunted the micro-switchesehand by connecting'the. re-

sistanceRz and grid G1 to ground'through'the conductor 220, armature 2H2, and-conductor 22 l. Thistemporarily locks the vacuum tube T1 in a conductive. condition by maintaining its grid G1 at ground. and cathode potential.

Aftera period of time, the length of which, as beforementionedis dependent upon theconstant of the timing circuit comprising the variable resistance R4 and the condenser G2, which had been connected together throughthe relay armature 20B and contact point 2t8and conductor 2.50, the potential of the grid G2 in the tube T2 will return .to its cut-off value, whereupon this tubewill be again rendered non-conductive. The resultant cessation of flow of current through the relay S2 will in turn allow the armatures. 212 and its to return to the. initial positions shown in. Figure-=9, cpening the circuits atcontacts 2M and 215. The following resultant de-energization of the solenoid S will allow valve V to return to its normal position and the punch 91 to rise to its open position after having completed a dimple. As the dimple punch rises in the squeezer, the micro-switch 68 is again allowed to close momentarily due to the resultant rise of plungers 49 and 56, again bringing the grid of tube T1 momentarily to ground potential following the opening of the lookout circuit contact 214. Thereafter after a period of time, determined by the constant of the timing circuit for the tube T1 comprising the condenser C1 and resistance R1, the grid G1 of T1 will return to cut-on potential. The resultant cessation of current flow through the relay S1 will allow the armature 295 to return to the position shown, re-establishing contact with point 267 and thereby discharging condenser C2 to ground potential in readiness for the next operating cycle. The time constant of the circuit comprising Ri-C1, is such that the brief time interval between the opening of contact 2M and the re-closing of micro-switch 65 is alone insufiicient to return tube T1 to its non-conductive condition.

It is obvious that, with the electronic circuit, as with the electric circuit hereinbefore described, a delay period is provided thereby, during which actuation of the micro-switches 55 and 66 by movement and adjustment of the sheet 11 and return of the dimpling punch after forming a dimple will not result in immediate repetition of the operating cycle. The time constant of the timing circuit Ri-Ci and R4Cz may be adjusted to suit the particular operating conditions obtaining by variation of either the resistances or the capacity of the condensers in the manner well known by those skilled in the art. However, adjustment of the constant of these timing circuits may be most conveniently made by employing variable resistances at R1 and R4.

Referring now to Figure 8, an optional version of the automatic die holder suitable for operation in conjunction with the electronic circuit of Figure 9 is shown. Here, instead of employing two micro-switches 65 and 66 which are fixed to the stationary body of the die holder, as shown in Figure l, a single micro-switch 225 is employed which is attached to the flange portions 33 at the bottom of the cut-out of the ring 45 and is movable therewith. The laterally extending actuating pin 63 is located in the plunger 54 at a higher position than that shown in Figure 4, which will enable it, upon upward relative movement, to contact the micro-switch actuating plunger 226. Electrical connection through the micro-switch 225 is made through the before mentioned lead conductors l6 and H. The action of the micro-switch 225 in the arrangement shown in Figure 8 is the same as that of the two micro-switches 65 and 66 shown in Figure 4. Thus, upon depression of the pilot pin 55, the plunger 54 will be lowered carrying with it the lateral pin 63 which will be moved further away from contact with the micro-switch actuating pin 225. The micro-switch 225 will thus remain open, with the electrical circuit remaining inoperative. If, thereafter, the pilot pin 55 is registered with a drilled hole in the sheet 98, and if sufficient sheet weight is placed upon the ring 45 to lower the micro-switch 225 together with the seat 33 upon which it is carried, to bring the micro-switch ac tuating plunger 226 into contact with the lateral pin 53, the electrical circuit between the conductors l t-I1 will thus be completed and the electrical circuit actuated to initiate the dimpling 10 cycle of operations, which occur as hereinbefore described in connection with the electronic circuit of Figure 9.

The present invention has for one of its advantages, the elimination of the foot pedal heretofore employed for either the initiation or the actuation of the dimpling tool. The elimnation of the manual control of the dimpler has resulted in the removal of a source of fatigue for the operator. Heretofore the uniformity of dimples produced by the manual control were dependent largely upon the pressure exerted by the operator. Slow, light pressure on the foot pedal produced shallow poorly defined dimples, while fast, heavy pressure produced deep, sharply defined dimples. The production of perfectly formed dimples re quired an intense concentration, and such coordination of eyes, hands and feet as obviously resulted in suficient nerve strain and fatigue to result in a substantially reduced rate of production with frequent mis-dimpling and damage to the sheet metal upon which the operations were be'ng performed. Damage was often done to the die and punch by rough operation of unskilled operators.

In the apparatus of the present invention due to the fact that no manual coordination or operation is required and by reason of the fact that it is impossible to actuate the dimpler until the work sheet is precisely positioned on the pilot pin, anyone without previous experience can produce perfectly formed dimples. Also, positively and uniformly formed dimples will always be produced due to the un form pressure obtained. While the present automatic control is illustrated for use with a dimpling tool, it is obvious that it may be employed in connection with any similar tool.

It is to be understood, therefore, that the foregoing is not to be lim'ting but may include any and all forms of methods and apparatus which are included within the scope of the claims.

I claim as my invention:

1. In combination with a tool for forming sheet metal, a trigger adjacent the forming portion of the tool and adapted to be actuated by contact with work material to be formed, a movable pilot member adjacent the forming portion of the tool and adapted to be retracted by improper contact with the material and to project upon registering with a reference element in the material to be formed, a power relay, a switching mechanism adjacent the forming portion of said tool, and means cooperatively associated with said trigger and pilot members to actuate said switching mechanism to cause said power relay to be actuated only when material is properly positioned with respect to said tool in contact with said trigger member and simultaneously in registration with said pilot member, and a time delay means associated with said power relay to limit the actuation of said tool to a single forming operation for each such proper position of the work material.

2. In combination with a tool for forming sheet metal, a trigger adjacent the forming portion of the tool and adapted to be actuated by contact with work material to be formed, a movable pilot member adjacent the forming portion of the tool and adapted to be actuated by contact with the material and to register with a reference element in the material to be formed, a pair of switches adjacent the forming portion of said tool, means associated with said trigger to close one of said switches and means associated with said pilot member to open the other of said switches, and control means actuated by said switches to cause 'a is sis'aa power to be applied to said tool'only when material is properly positioned with respect to said tool in contact with said trigger member and in registrati'on with said pilot member.

' 3. In combination with a tool for'for'min'g'sheet metal, a forming surface, a Support for said forming surface, a movable trigger carried by said support and'extending above the forming "surface of said tool in a position to be contacted by sheet v metal to be formed when placed on said tool in forming position, a retractable pilot member extending through said forming surface and adapted to be retracted by contact with sheet metal to be formed when said sheet metal is improperly positioned on the forming surface, and to register with and extend into an indexing deformation, in the sheet metal to be formed when said sheet metal is properly positioned on said forming surface, and a switching mechanism associated with said support adapted to be actuated by the combined movement of said pilot member and said trigger member.

6:. Apparatus according-to claim 3 and a power relay controlled by said switching mechanism to applypower to said tool only when material is properly positioned with respect to said tool in contact with said trigger member, and in registration with said pilot member.

5. Apparatus according to claim 2 and a time delay means associated with said control means to limit the actuation of said tool to a single forming operation for each position of the work material.

6. Apparatus in accordance with claim 2 and time delay means associated with said control means actuated by the said switches to limit the actuation of the tool to a single forming opera tion for each position of the work material, and means to reset the control means for'the next forming operation upon movement of said work material to a new forming position in the tool.

7 In combination with a tool for dimpling -preperforated sheet metal, a dimple forming surface,

a support for said surface, a movable trigger carried by said support and extending above the forming surface of said tool in a position to be contacted by sheet metal to bedimpled when placed on said tool in dimpling position, a retractablepilot pinextending through the center "of said'dimple forming urface-and adapted to be retracted by contact with sheet metal to be "dimpled when said sheet metal is improperly positioned on the forming surface, and to extend through a perforation in the sheet metal to be di'mpled when said sheet metal is properly positio'nedon' said forming surface, and a'switching mechanism associated with said support and adapted to be actuated by the combined movement of said pilot pin and said trigger member.

8. Apparatus inaccordance'with claim '7 and electric control means actuated by said switching "mechahismto cause power to "be applied to said tool only whenth'e tool is properly positioned with 'resp'e'ctto said tool in contact with said triggermember'a'nd inregist'rati'on with said pilot pin.

9. A dimplingtool of the class described comprising a punch carrying a male dimpling surface an'd a projecting pilot pin, a die having a'complementary dimpling surface, a central'movable pilot pin projecting from said die and retractable upon contact with the pilot pin of said punch to permit closing of said punch and die during the dimpling operation, a retractable support for the material 'tobe dimpled, said support being v so associated with said die that in its extended position it makes contact with the work only 'when the die pilotpin either projects through file of this :patent:

UNITED STATES PATENTS Number Name Date 1,233,699 "Peirce July 17, 1917 2,017,865 Morgan Oct. 22, 1935 2,328,919 -Merriman Sept. '7, 1943 

